Jon told me about this word after reading a 1999 Salon article about corporate naming, which said than when naming firm A Hundred Monkeys presented Jamcracker among the possible names for a client:
"I put the name up in front of their creative people," Manning says. "There were a couple of women sitting in. One of them got up and said, 'Oh, that's disgusting.' Another said, 'This is really sick.' I said, 'Excuse me, what are you talking about?' They said, 'We can't explain it, but that name is just creeping us out. We don't know what it is, but could you take it off the wall, please?'" Manning remains mystified by the incident. "There's apparently some strange, uncomfortable meaning attached to it in the minds of some women," he says. "God knows what that could be."
My first thought was that "Jamcracker" sounds like it should be slang for something sexual. For some reason I want to associate the word with flashers or Peeping Toms, though I know it has no such meaning. It doesn't creep me out as much as the women mentioned, though.

In addition to supplying the name for Jessicapierce's cat, there is now (June 2002) a Jamcracker, Inc. company, whose web site defines the word as:

  1. "an expert river driver who is stationed at a point where a log jam is feared.
  2. one who breaks up log jams.
  3. The leading provider of web-based application solutions."
I guess for them the problem-solving connotations of the definition outranked any creepy implications.

Update 9 April 2003: Any was kind enough to alert me to a discussion in the comments for the Slashdot book review of "F'd Companies" where this article was brought up and someone called davidmb enlightened us that "the women's reactions were a clue...A Jamcracker is a women who's having her period." Jam, crack -- oh. I'm guessing the corporate namers never heard that bit of slang.

Sources:
http://www.salon.com/media/col/shal/1999/11/30/naming/index.html (main article)
http://www.salon.com/media/col/shal/1999/11/30/naming/index4.html?x (actual quotation)
http://www.jamcracker.com
http://books.slashdot.org/books/03/01/16/2345206.shtml?tid=98